Why Prince William isn't supposed to fly in the same plane as Prince George and Princess Charlotte

It's all because of a time-old royal tradition

Fun fact: Although he often does it, Prince William is not actually supposed to fly in the same plane as his children.

That's right – when he travelled to Poland with Kate, George and Charlotte for the royal tour earlier this year, he was breaking an ancient royal rule by doing so.

It's not the first time he's bent the rules either – here are 10 more times Prince William and Kate Middleton ripped up the rule book.

Heirs to the throne aren't supposed to travel in the same aircraft, in order to protect the line of succession to the throne should there be an accident.

Technically, Prince George and Princess Charlotte should not travel in the same plane either, as they are third and fourth in line to the throne respectively.

However, it's not an official rule and so Prince William and his family tend to always travel together – but they do require the permission of the Queen to do so.

According to the BBC: 'While there is no official rule on this, and royal heirs have travelled together in the past, it is something that the Queen has the final say on.'

When Prince George accompanied his parents on their tour of Australia and New Zealand in 2014, Prince William first had to get Queen Elizabeth's permission for his son to fly in the same plane as him.

It's thought that the rule has become much more relaxed over the years due to vast improvements in technology and therefore safety.

Interesting stuff, right?